Fully hardened and tempered for long bit life under constant heavy-duty use. The tip is precision formed for proper use. Use when driving heat-treated or case-hardened screws such as sheet metal, self-tapping or self-drilling. Made of the highest quality S2 tool steel for durability. A proven sub-zero tempering process gives these bits extended life. Shank diameter 0.25; Shank 1/4". Bit set includes: (1) T10, (1) T15, (1) T20, (1) T25, (1) T30 and (1) T40.